[PATCH] D117502: [LV] Combine vector reductions parts in tree instead of serially.

[Florian Hahn via Phabricator via llvm-commits]

fhahn added a comment.

In D117502#3249197 <https://reviews.llvm.org/D117502#3249197>, @dmgreen wrote:

> Does this alter much? Or do we end up redistributing them anyway? https://godbolt.org/z/z4nf5hPna

It won't have a massive impact in general, but it shaves off a few cycles, depending on the interleave count.

AFAICT the redistributions done in the https://godbolt.org/z/z4nf5hPna are done by `ReassoicatePass`, which likes to turn parallel reduction trees into serial ones (? but that's a separate issue I think), like for `@float2`, which looks like it got serialized. I don't think any passes that run after the vectorizer try to improve the length of reduction chains: https://godbolt.org/z/v4K4aK3a1


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